The present invention relates to wheel sets for vehicles capable of travelling in either direction along a guide path, and including at least a front set and a rear set, each set having steerable load-carrying wheels.
More particularly, the invention relates to a wheel set of the type having a pair of load-carrying wheels that are steerable about parallel axes relative to a fixed portion, and two pairs of guide wheels for bearing laterally against the track, the pairs of guide wheels being situated on either side of the load-carrying wheels in the direction of travel along the track, and being carried by a common guide frame that is displaceable relative to the fixed portion, the fixed portion being constituted by a transverse box girder placed above the guide frame and provided with steering pivots for the load-carrying wheels, which pivots are placed beneath cushions providing suspension for the vehicle on the wheel set.
A wheel set of the above-defined type is already known from FR-A-2,675,105, in which the fixed portion is constituted by a central driving axle supporting the body of the vehicle via lateral arms and lateral pneumatic cushions. The driving axle receives motive power from a motor carried by the body of the vehicle. The guide frame is displaceable both in rotation and in translation relative to the fixed portion. The guide wheels serve as feelers for controlling the steering of the load-carrying wheels: rotation of the guide frame causes the load-carrying wheels to steer so as to follow the direction of the path, and translation thereof acts via hydraulic cylinders to cause the load-carrying wheels to steer excessively for the purpose of compensating for the lateral forces to which the vehicle is subjected. The lateral forces are therefore taken up by the load-carrying wheels and not by the guide wheels. The ability of the guide frame to move in translation requires the use of hydraulic cylinders and of the associated controls. It therefore tends to complicate the structure of the wheel set, and that would appear to be undesirable in the context of rail transport where safety requirements are particularly severe.